The present invention relates to an inlet distribution apparatus for process gases and liquids in a cocurrent downflow reactor.
In hydroprocessing, reforming and various chemical production reactors within a petroleum refinery or the like, fixed bed reactors featuring cocurrent downflow of gas or gas-liquid mixtures through beds of solid catalyst require efficient fluid distribution at the inlet of the reactor. Optimal reactor performance and control may be achieved only when the fluids are uniformly distributed across the entire catalyst bed area, so that all of the catalyst is contacted by the flowing reactant fluids.
Reactor flow distribution begins in the inlet nozzle where fluids are dispersed over the downstream trays or catalyst beds. These reactors are typically fed by a single inlet line approaching horizontally and connecting to a 90xc2x0 elbow directed downward into the reactor vessel. The elbow, attached to the vessel""s top flange, leads to an expanded cylindrical manway mounted on the hemispherical or elliptical reactor head. Directly below the vessel entrance is the inlet nozzle distributor.
An effective inlet nozzle distributor should accomplish at least four objectives. First, the distributor should erase all angular and radial asymmetries imparted by the approach piping, thereby achieving uniform coverage over the tray or solids bed below. In general, a flow bias will exist towards the outer wall of the inlet elbow, and for gas-liquid mixtures, this may result in phase segregation at the reactor inlet. Second, the hardware should reduce or break the entering fluid momentum to prevent high-velocity erosion of the shell, internals or solids bed. This deceleration is particularly important when the pre-distributor tray does not reach the reactor wall. Liquid contacting at high velocity can splash off this pre-distributor tray to the final distributor tray, thus compromising two-phase distribution. Third, the pressure drop across the inlet nozzle must be acceptable for optimal reactor flow rates. Finally, the distributor design must not permit excessive coking and solids accumulation.
For two-phase processes, poor fluid distribution will negatively impact the completeness and uniformity of catalyst wetting. This flow maldistribution will decrease effective catalyst activity and may lead to lateral temperature differences in the bed, leading to off-spec products, higher temperature requirements, poorer product selectivities and faster catalyst deactivation. In gas-phase reactors, ineffective distribution can create high-velocity eddies in the reactor head, leading to erosion of the solids bed.
U.S. Pat. No. 5,152,967 to Rossetti, et al. discloses the use of a vaned swirl chamber in a fixed-bed reactor quench zone located between two catalytic beds.
U.S. Pat. No. 5,462,719 to Pedersen, et al. discloses a method and apparatus for mixing two reactants within a column such as a process stream of both gas and liquid phases, and a quench gas. The apparatus is located beneath the lower end of an upper catalyst bed in a column (col. 3, lines 21-23).
A first object of the present invention is to provide an apparatus for imparting an overall rotational direction of flow to fluids entering a fixed bed reactor, so as to reduce or eliminate flow asymmetries and break fluid momentum entering the reactor.
A second object of the present invention is to provide such an apparatus which is easily retrofitted into existing fixed bed reactors, so as to minimize capital expenditures, while providing improved fluid flow within the reactors, so as to enhance the overall efficiency of the fixed bed reactor.
One embodiment of the present invention is directed to a fluid inlet nozzle for a downflow reactor which is a cylindrical housing having inlet and outlet openings and a swirl chamber disposed within said housing, whereby said swirl chamber imparts rotational motion to a fluid exiting said inlet nozzle.